Modern wall-hanging boilers burn natural gas and use the hot exhaust gas to heat water which circulates through radiators in different rooms to provide central heating for residential houses. The efficiency of such boilers may be as high as 95 to 99 percent depending on the water flow temperatures. However, sulfur contained in the fuel gas (e.g., natural gas) is oxidized during the combustion process and converted into sulfuric acid which corrodes the heat exchanger fins (or pins) once the acid condenses on the fin surface. Corrosion products deposit and accumulate in the narrow gaps between the fins (or pins) of the compact heat exchanger. Exhaust gas flow passage is hindered and the efficiency of the boiler may be reduced by more than 10 percent after as little as five thousand hours of operation.